Beau Mertens has had a mixed day at Caulfield yesterday, closing the gap on jockeys' premiership leader Craig Williams with a winning double but also copping a suspension and losing a race on protest.

Melbourne's leading apprentice, Mertens has drawn to within four wins of Williams on the Melbourne jockeys' premiership after notching his 50th metropolitan win for the season when bringing up his second winner at Caulfield. Both wins were for the Lindsay Park team aboard Boom Time and Miss Gunpowder.

But Mertens was also first across the line in the opening event on Quilate, only to lose the race on protest and also cop a suspension.

Mertens shifted out over the final 200 metres on Quilate and stewards ruled his shifting cost Ma Jones victory and reversed the placings after Ma Jones's rider Ben Allen fired in a protest.

Stewards later suspended Mertens for eight meetings, meaning he will miss one metropolitan fixture, next Saturday at Caulfield. His ban is due to begin after racing on Tuesday and he can return at Flemington on April 25.